Tyrosine phosphorylation patterns and size modification of the Helicobacter pylori CagA protein after translocation into gastric epithelial cells

Helicobacter pylori is one of the most common bacterial pathogens that caus es a variety of gastric diseases. During infection, the immune-dominant H. pylori CagA protein is translocated and tyrosine-phosphorylated in gastric epithelial cells. We compared tyrosine phosphorylation patterns of five Cag A variants by two-dimensional electrophoresis (2-DE) and immunoblotting stu dies. Tyrosine-phosphorylated CagA was detected as two distinct protein spe cies in strains P12, P227, G27 and 26695 suggesting that two tyrosine resid ues of CagA can be phosphorylated both separately and simultanously. Predic tion programs revealed the presence of three putative tyrosine phosphorylat ion motifs in the sequences of CagA. Mutations in these motifs were identif ied suggesting that only two putative phosphorylation-relevant tyrosines ar e present in each CagA variant. CagA of strain J99 was found to be unique b ecause essential codons were mutated in each of the three motifs and, conse quently, revealed no tyrosine phosphorylation signals at all. These finding s support the view that CagA from different H. pylori strains can be tyrosi ne-phosphorylated at one or two out of three predicted positions. Additiona lly, truncated CagA protein species of about 100-105 kDa (p100(CagA)) have been detected after infection with some of the H. pylori strains. The isoel ectric point determined by both 2-DE and sequence analysis suggested that p 100(CagA) represents the amino (N)-terminal part of the protein. Translocat ion, tyrosine phosphorylation and size modification of CagA might be involv ed in host signal transduction and development of gastric disease.